Wheel alignment equipment is used to measure the alignment of the wheels of a vehicle. Based on the measurements, adjustments to be made to the vehicle and wheels are determined in order to bring the wheels into alignment. As part of the alignment measurement process, the alignment equipment commonly measures the relative alignment of wheels disposed on each side of the vehicle separately (e.g., on a left side and a right side). In order to relate measurements taken on one side of the vehicle with measurements taken on the other/opposite side of the vehicle, the alignment equipment generally needs to have a precise reference for relating the measurements taken on the one side to the measurements taken on the other/opposite side.
Alignment systems include conventional aligners, visual alignments, and self-calibrating aligners. In conventional aligners, a toe gauge is provided in one wheel alignment head attached to a vehicle wheel on one side of the vehicle. The toe gauge can measure an angle to another toe gauge provided in another wheel alignment head that is attached to a wheel on the other side of the vehicle. The aligner can then relate alignment measurements taken on the one side of the vehicle with alignment measurements taken on the other side of the vehicle based on the toe gauge measurement.
However, the toe gauges used in conventional aligners are attached to the alignment heads, and generally require use of a boom extending from the alignment head to look around the wheel that it is attached to. The presence of such booms results in large, heavy, and expensive alignment heads, and the toe gauges can be obstructed easily by the vehicle body since they are in a fixed position on the alignment head (e.g., any rotation of the alignment head, for example resulting from the rolling forward or backward of the vehicle, may result in the toe gauge being obstructed).
In visual aligners (e.g., camera-based aligners), a solid beam mounted to a fixed structure (e.g., a shop wall) holds two alignment cameras each looking down a respective side of the vehicle. The relative position of the two alignment cameras is maintained fixedly by the solid beam and, once the relative position is measured and stored in memory, the relative position of the alignment cameras can be used to relate alignment measurements taken on the one side of the vehicle (by one alignment camera) with alignment measurements taken on the other side of the vehicle (by the other alignment camera).
However, the cameras of the visual aligners are fixedly attached to a large beam. The large beam can get in the way of shop operations, and the presence of the large beam results in a system that is large, heavy, and expensive. Additionally, the large beam has minimum configurations options, and any deformation of the beam results in alignment measurement inaccuracies.
In the case of self-calibrating aligners, a calibration camera is provided in addition to two alignment cameras each looking down a respective side of the vehicle. The calibration camera has a fixed and known relative position to one of the two alignment cameras, and the calibration camera is oriented so as to point across a width of the vehicle towards the other of the two alignment cameras. Specifically, the calibration camera is oriented so as to point towards a calibration target that is attached to the other alignment camera, where the calibration target itself has a fixed and known relative position to the other alignment camera. In this set-up, the calibration can, as often as is required, obtain an image of the calibration target. In turn, based on the known relative positions between the calibration camera and the one alignment camera and between the calibration target and the other alignment camera, the alignment system can precisely determine the relative positions of the two alignment cameras. The determined relative position information is used to relate measurements taken by the alignment cameras on both sides of the vehicle.
However, while the self-calibrating aligners address some of the drawbacks of the conventional and visual aligners noted above, the self-calibrating aligners rely on a calibration camera or a calibration target being attached to each alignment camera. As a result, the aligner generally needs to be set-up in such a manner that the calibration camera (attached to one alignment camera) can see the calibration target (attached to the other alignment camera) while the alignment cameras are each oriented to see vehicle wheel alignment targets on a respective side of the vehicle. This set-up complexity restricts the acceptable locations of the alignment cameras (each having one of the calibration camera and the calibration target attached thereto), and limits some of the acceptable locations where the system can be used.
In order to address the drawbacks detailed above, there exists a need for a side-to-side reference that can be used when measuring the alignment of a vehicle.